Patent DE-10313213-A1 (DE)
Title: Process for partial gas phase oxidation of propene to acrylic acid involves oxidation of propene-containing gas mixture; and then oxidation of the resultant acrolein-containing product over fixed catalyst bed zones at different temperatures
IPC: C07C51/25
Filed: 2003-03-25
Abstract: Partial gas phase oxidation of propene to acrylic acid involves oxidation of reaction gas mixture of propene, molecular oxygen and at least one inert gas in a first reaction stage over several fixed catalyst bed zones, in temperature zones A and B; followed by oxidation of the resultant acrolein containing product over several fixed catalyst bed zones, in temperature zones C and D. Partially oxidizing propene to acrylic acid in the gas phase under heterogeneous catalysis by conducting a starting reaction gas mixture 1 comprising propene, molecular oxygen and at least one inert gas in a first reaction stage over a fixed catalyst bed 1 (C1) whose active composition is at least one multimetal oxide comprising Mo, Fe or Bi, in such a way that (C1) is arranged in two spatially successive temperature zones A and B having temperature of 290 - 380[deg]C, (C1) consists of at least two spatially successive fixed catalyst bed zones and the volume specific activity within one fixed catalyst bed zone is constant and increases sharply in the flow direction of the mixture 1 at the transition from one fixed catalyst bed to another bed zone, the temperature of A extends to 40 - 80 mol % up to a conversion of the propene, on single pass of the starting reaction mixture 1 through (C1), the propene conversion is >= 90 mol % and the selectivity of acrolein formation and also of acrylic acid by production taken together and based on converted propene are >= 90 mol %, the sequence in time in which the mixture 1 flows through the A and B corresponds to the alphabetic sequence of the A and B, the hourly space velocity of the propene contained in the starting mixture 1 on (C1) is >= 90 l (STP) of propene/l of (C1).h, the difference between T max for A and B, formed from the highest temperature T max for A, which (C1) has within the zone A and the highest temperature T max for B, which (C1) has within the zone B is >= 0[deg]C; and optionally reducing the temperature of the product gas mixture leaving the first reaction stage by cooling and optionally adding molecular oxygen and/or inert gas to the product gas mixture, and afterward conducting the product gas mixture as a starting reaction gas mixture 2 (C2) comprising acrolein, molecular oxygen and at least one inert gas, and containing the molecular oxygen and the acrolein in a molar ratio of >= 0.5 in a second reaction stage over (C2) whose active composition is at least one multimetal oxide of Mo and V, in such a way that (C2) is arranged in two spatially successive temperature zones C and D having temperature of 230 - 320[deg]C, (C2) consists of at least two spatially successive fixed catalyst bed zones and the volume specific activity within one fixed catalyst bed zone is constant and increases sharply in the flow direction of the mixture 2 at the transition from one fixed catalyst bed to another bed zone, the temperature of C extends to 45 - 85 mol % up to a conversion of the acrolein, on single pass of the starting reaction mixture 2 through (C2), the acrolein conversion is >= 90 mol % and the selectivity of acrylic acid formation is >= 80 mole % based on propene converted over both reaction stages, the sequence in time in which the mixture 2 flows through the C and D corresponds to the alphabetic sequence of the zones C and D, the hourly space velocity of the acrolein contained in the starting mixture 2 on (C2) is >= 70 l (STP) of acrolein /l of (C2).h, the difference between T max for C and D, formed from the highest temperature T max for C, which the mixture has within the zone C and the highest temperature T max for D, which the mixture has within the zone D is >= 0[deg]C. The transition from A to B in (C1) and from C to D in (C2) within reaction stage does not spatially coincide with a transition from one fixed bed zone to another zone.